From Charles Poliquin
Do sled training to lose fat, build muscle, and improve conditioning. Sled training is similar to sprint training in that it is a powerful tool such that the payoff is worth the pain and effort required.
A new British study had strength-trained males perform a weighted sled training session and then tested hormone levels, markers of muscle damage, and neuromuscular strength at various points after the workout. The workout consisted of five sets of two 20-meter sled pulls with the sled loaded with 75 percent of body mass. The drag position had participants facing the sled and moving backwards, emphasizing concentric muscle actions in the legs.
Results showed the following:
• Neuromuscular strength as measured by a countermovement vertical jump was reduced for 1 hour after the workout, but it was recovered to baseline levels by 3 hours after the workout. The immediate reduction in strength and power were likely due to depleted phosphocreatine and acid-base disruption, as well as hydrogen ion accumulation.
• The subjects recovered neuromuscular strength quickly, which indicates is due to the fact that sled dragging uses concentric contractions that don’t cause significant muscle damage. A traditional weight training workout that includes the eccentric motion as well would produce much more muscle damage, requiring a much longer recovery time.
• The lack of muscle damage was confirmed with no evidence of a change in the biomarker, creatine kinase.
• There was a six-fold increase in blood lactate after the workout, indicating a large metabolic stress that could be effective for promoting fat loss. Lactate buildup is associated with a large elevation in growth hormone and IGF-1.
• Testosterone increased by 38 percent at 15 minutes
post-workout. Testosterone was also elevated at 24 hours post-training, which could represent a rebound effect to aid recovery from intense training. Researchers suggest this is a favorable response that could improve subsequent motivation to train, increase competitive drive, and reduce fear.
• Cortisol was increased 54 percent at 15 minutes post-workout, but it declined below baseline at 3 hours, indicating an effective recovery. The T:C ratio indicated a positive training stressor.
Researchers suggest this type of training could lead to beneficial changes in body composition, without a major reduction in strength performance. Sled training will induce glycogen depletion if volume and intensity are high enough, while applying significant metabolic stress. However, since there was no evidence of muscle damage, glycogen resynthesis wouldn’t be hindered as long as athletes take advantage of the post-workout recovery period. A second competition or workout could be performed the same day, for example.
West, D., et al. The Metabolic, Hormonal, Biomechanical, and Neuromuscular Function Responses to a Backward Sled Drag Training Session. Journal of Strength and Conditioning Research. 2013. Published Ahead of Print.